Update flags passed to make

Remove more GCC-specific flags, TARGET_(arm|thumb)_CFLAGS now contains
pre-filtered clang flags, and GLOBAL_CLANG_CFLAGS_NO_OVERRIDE now
contains all flags instead of just the clang additional flags.

Test: m
Change-Id: I61e4c5a92113d4ff3b95261783269dc1d226c57a